This invention relates in general to electrophotographic imaging members, and more specifically, to the use of an aqueous dispersion or latex of a mixture of certain polyurethanes to form an adhesive layer during the preparation of an electrophotographic imaging member and to electrophotographic imaging members containing this adhesive layer.
In the art of electrophotography an electrophotographic plate comprising a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the imaging surface of the photoconductive insulating layer. The plate is then exposed to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated area. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electrostatically attractable toner particles on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving member such as paper. This imaging process may be repeated many times with reusable photoconductive insulating layers.
The electrophotographic imaging member may be multilayered photoreceptor that comprises a substrate, a conductive layer, a charge blocking layer, an adhesive layer, a charge generating layer, and a charge transport layer.
Although excellent toner images may be obtained with multilayered photoreceptors, it has been found that when attempts to fabricate multilayered photoreceptors in which the charge generating layer is a thin homogeneous layer formed by vacuum deposition or sublimation on a solvent soluble or solvent swellable adhesive layer, a pattern of cracks form in the charge generating layer when coating solutions of charge transport material are applied to the thin charge generating layer. The pattern of cracks print out during development and the pattern is visible in the final xerographic copy. This pattern of cracks prevents use of these photoreceptors in systems that require long service life flexible belt photoreceptors in compact imaging machines that employ small diameter support rollers for photoreceptor belt systems operating in a very confined space. Small diameter support rollers are also highly desirable for simple, reliable copy paper stripping systems which utilize the beam strength of the copy paper to automatically remove copy paper sheets from the surface of a photoreceptor belt after toner image transfer. Unfortunately, small diameter rollers, e.g., less than about 0.75-inch (19-mm) diameter, raise the threshold of mechanical performance criteria to such a high level that photoreceptor belt seam failure can become unacceptable for multilayered belt photoreceptors. Thus, in advanced imaging systems utilizing multilayered belt photoreceptors, cracking and delamination has been encountered during belt cycling over small diameter rollers. Frequent photoreceptor cracking and delamination has a serious impact on the versatility of a photoreceptor and prevents its use in automatic electrophotographic copiers, duplicators and printers.